Copper foil used in the manufacture of printed circuit boards is usually bonded to a dielectric base material and various proposals have been made for improving the strength of the bond between the copper foil and the base material.
For example it is now well-established practice to apply copper dendrites to the matt surface of the foil, said dendrites often being reinforced or partially encapsulated with a continuous, coherent layer of copper. Several subsequent electrodeposited layers may then follow to achieve a bond of desired strength and one which will be largely unaffected by soldering. Metallic layers of, for example, zinc, brass or nickel may be present to separate the copper dendrites from the reactive resins in the dielectric base material. It is often difficult to control the size and distribution of the dendrites in the primary copper layer and it has therefore been proposed to add various agents to the copper of said layer in an attempt to effect such control, a preferred additive being arsenic. In such a case, a nodular or dendritic layer of metal comprising an alloy of oxidised copper with arsenic is electrodeposited onto a matt surface of the copper foil from a bath containing copper sulphate and arsenic values.
However reliable control in the growth of the dendrites, particularly the larger dendrites, is still not completely satisfactory.